Vibration welding systems and methods

ABSTRACT

A method for forming a fiber-reinforced thermoplastic hollow structure may comprise: abutting a first surface of a first flange of a shell and a second surface of a second flange of the shell with a mating component; disposing an end block laterally adjacent to the shell; applying a first load to a sidewall of the shell; applying a second load to the second flange of the shell; and vibrating one of the shell or the mating component while keeping a non-vibrating component stationary, the non-vibrating component including one of the shell or the mating component.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of, and claims priority to and thebenefit of, U.S. Non-Provisional application Ser. No. 17/554,137, filedDec. 17, 2021 entitled VIBRATION WELDING SYSTEMS AND METHODS, which isincorporated in its entirety by reference herein for all purposes.

FIELD

The present disclosure relates generally to systems and methods forvibration welding hollow structures, and more specifically to systemsand methods for vibration welding without a direct load applied to anouter weld area for aircraft components.

BACKGROUND

Aircraft are typically equipped with interior components and flightcontrol surfaces. Flight control surfaces are utilized to maneuver theaircraft during flight as well as provide high lift surfaces to increaselift at low airspeed. Interior components vary significantly but oftenutilize hollow structures to reduce weight and decrease manufacturingcosts. Vibration welding is utilized to couple a hollow structure to anadjacent component. Vibration welding operates at lower frequencies andhigher amplitudes relative to ultrasonic welding. Additionally, a largeclamping force is typically applied to each flange of a hollow structurethat is being welded to an adjacent component.

SUMMARY

A method for forming a fiber-reinforced thermoplastic hollow structureis disclosed herein. The method may comprise: abutting a first surfaceof a first flange of a shell and a second surface of a second flange ofthe shell with a mating component; disposing an end block laterallyadjacent to the shell; applying a first load to a sidewall of the shell;applying a second load to the second flange of the shell; and vibratingone of the shell or the mating component while keeping a non-vibratingcomponent stationary, the non-vibrating component including one of theshell or the mating component.

In various embodiments, the vibrating generates heat between the firstsurface of the first flange and the mating component and generates heatbetween the second surface of the second flange and the matingcomponent.

In various embodiments, a direct load is not applied to the firstflange.

In various embodiments, the vibrating forms a weld seam between thefirst flange and the mating component. The weld seam may be between 20%and 80% of a lateral length of the first flange.

In various embodiments, the shell comprises a fiber-reinforcedthermoplastic material including continuous fibers.

In various embodiments, the method further comprises stamp forming aplurality of ridges into the first flange prior to the abutting.

In various embodiments, the method further comprises one of over moldingor insert molding stiffening members between the first flange and anadjacent sidewall of the first flange prior to the abutting.

In various embodiments, the method further comprises stamp formingstiffening ribs into an adjacent sidewall of the first flange prior tothe abutting.

A method for forming a fiber-reinforced thermoplastic hollow structureis disclosed herein. The method may comprise: abutting a first surfaceof a first flange of a shell and a second surface of a second flange ofthe shell with a mating component; applying a first load to a sidewallof the shell and a second load to the second flange without applying aload to the first flange; restraining lateral movement of the firstflange; and vibrating one of the mating component or the shell in alongitudinal direction to join at least a portion of the first flange tothe mating component.

In various embodiments, the vibrating includes oscillating a vibratingcomponent that comprises one of the mating component or the shellrelative to a non-vibrating component that comprises one of the matingcomponent or the shell.

In various embodiments, the method further comprises disposing an endblock laterally adjacent to the shell.

In various embodiments, the shell comprises at least one of glassfibers, carbon fibers, aramid fibers, basalt fibers, mineral fibers,fibers from renewable raw materials, metal fibers and polymer fibers.

In various embodiments, the shell comprises a thermoplastic materialcomprising at least one of polyimide (PA), polypropylene (PP),polyethylene (PE), polyoxymethylene (POM), polyphenylene sulphide (PPS),polyether ether ketone (PEEK), polyetherimide (PEI), polyethyleneterephthalate (PET), polyphthalamide (PPA), Poly ether ketone ketone(PEKK), Poly aryl ether ketone (PAEK).

A fiber-reinforced thermoplastic hollow structure is disclosed herein.The fiber-reinforced thermoplastic hollow structure may comprise: ashell comprising a first flange, a second flange, and sidewalls, theshell comprising a fiber-reinforced thermoplastic material; and a matingcomponent coupled to the first flange and the second flange andincluding a first internal surface, and the first internal surface andinternal surfaces of the sidewalls defining a cavity, the first flangeand the mating component defining a first weld seam, the first weld seambeing between 20% and 80% of a lateral length of the first flange.

In various embodiments, the first weld seam is between 20% and 60% ofthe lateral length of the first flange.

In various embodiments, the second flange and the mating componentdefine a second weld seam, the second weld seam being between 90% and100% of a second lateral length of the second flange.

In various embodiments, at least one of the first flange and the secondflange further comprises a plurality of stiffening ridges.

In various embodiments, the fiber-reinforced thermoplastic hollowstructure further comprises stiffening ribs disposed at least one ofbetween the first flange and an adjacent sidewall and between the secondflange and an adjacent sidewall in the sidewalls of the shell.

The foregoing features and elements may be combined in variouscombinations without exclusivity, unless expressly indicated hereinotherwise. These features and elements as well as the operation of thedisclosed embodiments will become more apparent in light of thefollowing description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the present disclosure is particularly pointed outand distinctly claimed in the concluding portion of the specification. Amore complete understanding of the present disclosure, however, may bestbe obtained by referring to the detailed description and claims whenconsidered in connection with the drawing figures, wherein like numeralsdenote like elements.

FIG. 1A illustrates a perspective view of a shell and a mating componentprior to vibration welding, in accordance with various embodiments;

FIG. 1B illustrates a perspective view of a shell and a mating componentcoupled together to form a hollow structure via vibration welding, inaccordance with various embodiments;

FIG. 1C illustrates a cross-sectional view of a shell and a matingcomponent during vibration welding, in accordance with variousembodiments;

FIG. 2 illustrates a method of vibration welding, in accordance withvarious embodiments;

FIG. 3 illustrates a perspective view of a shell and a mating componentcoupled together, in accordance with various embodiments;

FIG. 4 illustrates a perspective view of a shell, in accordance withvarious embodiments;

FIG. 5 illustrates a perspective view of a shell, in accordance withvarious embodiments; and

FIG. 6 illustrates a perspective view of a shell, in accordance withvarious embodiments.

DETAILED DESCRIPTION

The detailed description of exemplary embodiments herein makes referenceto the accompanying drawings, which show exemplary embodiments by way ofillustration. While these exemplary embodiments are described insufficient detail to enable those skilled in the art to practice theinventions, it should be understood that other embodiments may berealized and that logical changes and adaptations in design andconstruction may be made in accordance with this invention and theteachings herein. Thus, the detailed description herein is presented forpurposes of illustration only and not for limitation. The scope of theinvention is defined by the appended claims. For example, the stepsrecited in any of the method or process descriptions may be executed inany order and are not necessarily limited to the order presented.Furthermore, any reference to singular includes plural embodiments, andany reference to more than one component or step may include a singularembodiment or step. Also, any reference to attached, fixed, connected orthe like may include permanent, removable, temporary, partial, fulland/or any other possible attachment option. Additionally, any referenceto without contact (or similar phrases) may also include reduced contactor minimal contact. Surface shading lines may be used throughout thefigures to denote different parts but not necessarily to denote the sameor different materials. In some cases, reference coordinates may bespecific to each figure.

In general, the example shells and mating components used to form ahollow structure as described herein may be used with control surfaces,such as aircraft wings, stabilizers, or elevators, among otheraerodynamic surfaces of an aircraft. Some examples of common names forthese surfaces known to those practiced in the arts include but are notlimited to flaps, ailerons, rudders, elevators, stabilators, elevons,spoilers, lift dumpers, speed brakes, airbrakes, trim tabs, slats,flaperons, spoilerons, and canards. These are henceforth referred to ascontrol surfaces. In general, control surfaces may direct air flowduring maneuvering and in-flight aircraft attitude adjustments. Theexample control surfaces described herein may provide increasedresistance to impact damage than some known control surfaceconstructions. Further, the example methods for manufacturing controlsurfaces described herein include fewer and lighter components than someknown control surfaces. Thus, the example control surfaces describedherein provide increased fuel efficiency and/or range to aircraft. Stillfurther, the example control surfaces may be manufactured using anautomated skin/stiffener manufacturing process, as described herein,which optimizes material usage and reduces cycle time.

Although described with respect to control surfaces, the presentdisclosure is not limited in this regard. For example, shells and matingcomponents coupled together in accordance with the systems and methodsdisclosed herein may be used for aircraft interior components like seatbacks, urban aerial mobility (UAM) components, or the like.

A thermoplastic material including a fiber-reinforced structure, asdescribed herein, includes a structural body comprising skin members. Invarious embodiments, the skin members include a continuous fiberreinforced fabric, or unidirectional tape based laminate, and athermoplastic resin. The reinforcing fiber, or a combination ofreinforcing fibers, to be used for the fiber-reinforced structure has noparticular limitations with respect to the type thereof, and examplesthereof include metal fibers, such as an aluminum fiber, a brass fiber,and a stainless steel fiber, carbon fibers (including graphite fibers),such as polyacrylonitrile (PAN)-based carbon fibers, rayon-based carbonfibers, lignin-based carbon fibers, and pitch-based carbon fibers,insulating fibers, such as glass fiber, organic fibers, such as aramidfibers, polyparaphenylene benzoxazole (PBO) fibers, polyphenylenesulfide fibers, polyester fibers, acrylic fibers, nylon fibers, andpolyethylene fibers, and inorganic fibers, such as silicon carbidefibers and silicon nitride fibers. Fibers prepared by applying surfacetreatment to these fibers are also available. Examples of the surfacetreatment include treatment with a coupling agent, treatment with asizing agent, treatment with a binder, and adhesion treatment with anadditive in addition to deposition treatment with conductive metal.

In the disclosure, the thermoplastic resin to be used for a matingcomponent and/or a shell may be either semi-crystalline or amorphous.

Examples of the semi-crystalline thermoplastic resin include polyester,polyolefin, polyoxymethylene (POM), polyamide (PA), polyarylene sulfide,polyketone (PK), polyetherketone (PEK), polyether ether ketone (PEEK),polyether ketone ketone (PEKK), polyvinylidene fluoride (PVDF),polytetrafluoroethylene (PTFE), polyaryletherketone (PAEK), polyethernitrile (PEN), fluororesin, and liquid crystal polymer (LCP). Examplesof the polyester include polyethylene terephthalate (PET), polybutyleneterephthalate (PBT), polytrimethylene terphthalate (PTT), polyethylenenaphthalate (PEN), and liquid crystal polyester. Examples of thepolyolefin include polyethylene (PE), polypropylene (PP), andpolybutylene. Examples of the polyarylene sulfide include polyphenylenesulfide (PPS). Examples of the fluororesin includepolytetrafluoroethylene.

Examples of the amorphous thermoplastic resin include polystyrene,polycarbonate (PC), polymethyl methacrylate (PMMA), polyvinyl chloride(PVC), polyphenylene ether (PPE), polyimide (PI), polyamide imide (PAI),polyetherimide (PEI), polysulfone (PSU), polyether sulfone (PES), andpolyarylate (PAR). The thermoplastic resin to be used for the controlsurface also may be phenoxy resin, polystyrene, polyolefin,polyurethane, polyester, polyamide, polybutadiene, polyisoprene,fluorine resin, acrylonitrile, and other thermoplastic elastomers, andcopolymers and modified resin thereof.

Disclosed herein is a method of vibration welding without applying adirect load to a flange that is welded to a mating component. The flangeis an element of a shell being coupled to the mating component viavibration welding. The flange is compressed, via the method disclosedherein, from a nearby area, which generates a force on a weld area ofthe flange and the mating component sufficient to weld the flange to themating component. In this regard, tooling costs may be reduced, avibration welding process may be simplified, and/or a high weld strengthbetween the flange and the mating component may be maintained.

Referring now to FIG. 1A, a perspective view of a shell 110 and a matingcomponent 120 prior to vibration welding is illustrated in accordancewith various embodiments. In various embodiments, the shell 110 and themating component 120 both comprise a fiber reinforced thermoplasticmaterial. The shell 110 may be formed from a first continuous fiberreinforced fabric or uni-directional tape based laminate, as describedherein. The mating component 120 may be formed from a second continuousfiber reinforced fabric, as described herein. In various embodiments,the second continuous fiber reinforced fabric is the same or similarmaterial as the first continuous fiber reinforced fabric. In variousembodiments, the shell 110 and/or the mating component 120 may both beformed of multiple layers of fiber reinforced fabric. The presentdisclosure is not limited in this regard. In various embodiments, one ofthe shell 110 and the mating component 120 may comprise afiber-reinforced thermoplastic material and the remaining component maycomprise any other material, such as a metal alloy (e.g., nickel-basedalloy, titanium-based alloy, aluminum-based alloy, iron-based alloy,etc.). The present disclosure is not limited in this regard.

In various embodiments, the shell 110 and the mating component 120 maybe formed by combining fiber fillers and thermoplastic resin at apre-selected ratio to form a thermoplastic composite material withcontinuous fiber reinforcement. For example, the shell 110 and/or matingcomponent 120 may be formed using automated fiber placement or automatedtape laying. The pre-selected ratio may have any percentage or ratio offiber filler to resin, such as 60% fiber filler and 40% resin. Themixture may range from 0% fiber filler and 100% resin to 80% fiberfiller and 20% resin. In this regard, shell 110 and/or the matingcomponent 120 may be continuous fiber reinforced. However, it iscontemplated herein that shell 110 and the mating component 120 may bediscontinuous fiber reinforced, in accordance with various embodiments.

In various embodiments, the shell 110 comprises a first flange 112 and asecond flange 114.

The first flange 112 and the second flange 114 are configured to bevibration welded to the mating component 120 without a direct load beingapplied to the first flange 112 as described further herein.

In various embodiments, the shell 110 further comprises sidewalls 116.With reference now to FIG. 1B, internal surfaces of the sidewalls 116and an internal surface of the mating component 120 define a cavity 102of a hollow structure 100 in response to being coupled together via thesystems and methods disclosed herein. Although illustrated as comprisingperpendicular sidewalls to form a substantially square cross-section forthe cavity 102, the present disclosure is not limited in this regard.For example, sidewalls 116 may comprise acute or obtuse angles and/ormay define various types of cross-sections, such as trapezoidal,polygonal, hexagonal, or the like and still be within the scope of thisdisclosure. In various embodiments, each flange (e.g., first flange 112and second flange 114) extends laterally (i.e., in the X-direction) froman adjacent sidewall (e.g., sidewall 118 for first flange 112 andsidewall 116 for flange 114). In various embodiments, a centerlinethrough the cavity 102 (i.e., in the Z direction) may define alongitidudinal axis for the hollow structure 100 from FIG. 1B.

Referring now to FIG. 1C, a system 101 for coupling the shell 110 to themating component 120 via vibration welding is illustrated, in accordancewith various embodiments. With combined reference to FIGS. 1C and 2 , amethod 200 of coupling the shell 110 to the mating component 120comprises abutting a first surface 111 of the first flange 112 and asecond surface 113 of the second flange 114 with the mating component120 (step 202). In various embodiments, the first surface 111 and thesecond surface 113 may abut a single surface (e.g., a singular planarsurface 122) of the mating component 120; however, the presentdisclosure is not limited in this regard. For example, with briefreference to FIG. 3 , a first surface 311 of a first flange 312 of ashell 310 may abut a first surface 321 of a mating component 320 and asecond surface 313 of a second flange 314 of the shell 310 may abut asecond surface 322 of the mating component (i.e., where the secondsurface 322 is in a different plane from the first surface 321) andstill be within the scope of this disclosure.

The method 200 further comprises disposing an end block 103 laterallyadjacent to the first flange 112 (i.e., the flange where a load will notbe applied) of the shell 110 (step 204). Although illustrated as beingdisposed adjacent to the first flange 112, the present disclosure is notlimited in this regard. For example, the first flange 112 could beoriented inward (i.e., into the cavity 102 from FIG. 1B) and still bewithin the scope of this disclosure. In this regard, the end block 103would be disposed laterally adjacent to a sidewall 118 of the sidewalls116. The end block 103 is configured to restrain lateral movement (i.e.,movement in the −X direction) during vibration welding as describedfurther herein. In this regard, a lateral position of a weld line mayremain constant during the welding process, in accordance with variousembodiments.

The method 200 further comprises applying a first load F1 to a sidewall117 of the sidewalls 116 and a second load F2 to the second flange 114(step 206). Each of the loads F1 and F2 may be at least generallydirected toward the mating component 120. In various embodiments, thefirst load F1 applied to the sidewall 117 may be substantiallyperpendicular to a plane defined by the sidewall 117. In variousembodiments, in response to the plane defined by the sidewall 117 beingcontoured, a plurality of local forces may be applied which may besubstantially perpendicular to the sidewall 117 at a local point wherethe force is applied. “Substantially perpendicular” as defined herein isbetween 60° and 90°, or between 70° and 90°, or between 80° and 90°. Invarious embodiments, a contact surface of the sidewall 117 configured toreceive the first load F1 may be substantially co-planar with the firstsurface 111 of the first flange 112. “Substantially co-planar” asreferred to herein is between 0° and 30°, or between 0° and 20°, orbetween 0° and 10°, in accordance with various embodiments.

Although illustrated as applying the first load F1 and the second loadF2 in a similar direction, the present disclosure is not limited in thisregard. For example, with brief reference to FIG. 3 , a load F3 may beapplied substantially perpendicular to sidewall 317 and a load F4 may beapplied substantially perpendicular to the second flange 314 during themethod 200 for forming the hollow structure 300. In this regard, theload applied to the sidewall (e.g., a non-mating flange), may besubstantially perpendicular to a mating surface of a non-loaded wall(e.g., first surface 311 of first flange 312. In this regard, the loadF3 supplied to sidewall 317 supplies a sufficient force, combined withan end block 103 from FIG. 1C positioned against the side of flange 312and component 320 preventing lateral motion of the first flange 312, tojoin the first flange 312 to the mating component 320 during step 208 asdescribed further herein.

The method 200 further comprises vibrating the mating component 120while keeping the shell 110 stationary (step 208). Although described asvibrating the mating component 120 relative to the shell 110, thepresent disclosure is not limited in this regard. For example, invarious embodiments, the shell 110 may be vibrated while the matingcomponent 120 is kept stationary. In various embodiments, “vibrating” asdescribed herein refers to translating a component (e.g., the matingcomponent 120 or the shell 110) relative to the other component back andforth (e.g., oscillating) in a longitudinal direction (i.e., alternatingbetween the Z direction and the −Z direction in FIG. 1C) to generatefriction heat between the first surface 111 of the first flange 112 andthe mating component 120 and the second surface 113 of the second flange114 and the mating component 120. In this regard, the friction heatfuses at least a portion of the first surface 111 of the first flange112 and the second surface 113 of the second flange 114 to the matingcomponent 120.

In various embodiments, a weld formed on the non-loaded flange (e.g.,the first flange 112) may only be a partial lateral length (i.e.,measured in the X direction from an adjacent sidewall) of the flange.For example, welding a shell 110 with a flange length of 0.25 inches(0.635 cm) may result in a weld seam of approximately 0.10 inches (0.254cm). In various embodiments, a weld seam may be between 20% and 80% of alateral length (i.e., in the X-direction) of a non-loaded flange, orbetween 20% and 60%, or between 25% and 50% by the method 200 disclosedherein. Although the entire flange of the non-loaded flange (e.g., firstflange 112) may not weld to the mating component, the partial weld seammay be sufficient for loading of the hollow structure 100 from FIG. 1B.For example, in some real cases the torsional test data of a resultanthollow structures 100 formed via method 200 from FIG. 2 resulted in thehollow structure 100 buckling, and ultimately failing, prior to disbondof the weld seam formed from the method 200. In this regard, thedecrease in weight and cost of manufacturing the hollow structure 100outweigh any reduction in structural capabilities of the weld formed bythe method 200 disclosed herein. In contrast to the non-loaded flange,the weld formed on the loaded flange (e.g., the second flange 114) maybe between 90% and 100% of a lateral length of the flange, between 95%and 100% of a lateral length of the flange, or approximately an entirelateral length of the flange, in accordance with various embodiments.

In various embodiments, by not having to apply a direct load to a flange(e.g., first flange 112) that is being friction welded to a matingcomponent 120, more complex hollow structures (e.g., hollow structure300 from FIG. 3 ) may be manufactured in a simpler manner and/or at alower expense relative to typical vibration welding processes.

In various embodiments, to further facilitate thinner shells beingcoupled to mating components, a stiffening structure may be coupled tothe first flange 112 and an adjacent sidewall 118 and/or a stiffeningstructure may be coupled to the flange 114 and an adjacent sidewall ofthe sidewalls 116. For example, with reference now to FIG. 4 , aplurality of stiffening ridges 432 may be stamp formed into a firstflange 412 of a shell 410 prior to performing the vibration weldingmethod 200 from FIG. 2 . With reference now to FIGS. 5 and 6 ,stiffening ribs 532 may be over molded or in-molded between a firstflange 512 and an adjacent sidewall 515 of a shell 510 (FIG. 5 ) orstiffening ribs 632 may be stamp formed into an adjacent sidewall 615 ofa first flange 612 of a shell 610 (FIG. 6 ) to further facilitatethinner shells being coupled to mating components as described herein.

Benefits, other advantages, and solutions to problems have beendescribed herein with regard to specific embodiments. Furthermore, theconnecting lines shown in the various figures contained herein areintended to represent exemplary functional relationships and/or physicalcouplings between the various elements. It should be noted that manyalternative or additional functional relationships or physicalconnections may be present in a practical system. However, the benefits,advantages, solutions to problems, and any elements that may cause anybenefit, advantage, or solution to occur or become more pronounced arenot to be construed as critical, required, or essential features orelements of the inventions. The scope of the inventions is accordinglyto be limited by nothing other than the appended claims, in whichreference to an element in the singular is not intended to mean “one andonly one” unless explicitly so stated, but rather “one or more.”Moreover, where a phrase similar to “at least one of A, B, or C” is usedin the claims, it is intended that the phrase be interpreted to meanthat A alone may be present in an embodiment, B alone may be present inan embodiment, C alone may be present in an embodiment, or that anycombination of the elements A, B and C may be present in a singleembodiment; for example, A and B, A and C, B and C, or A and B and C.Different cross-hatching is used throughout the figures to denotedifferent parts but not necessarily to denote the same or differentmaterials.

Systems, methods and apparatus are provided herein. In the detaileddescription herein, references to “one embodiment,” “an embodiment,” “anexample embodiment,” etc., indicate that the embodiment described mayinclude a particular feature, structure, or characteristic, but everyembodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed. After reading the description, it will be apparent to oneskilled in the relevant art(s) how to implement the disclosure inalternative embodiments.

Furthermore, no element, component, or method step in the presentdisclosure is intended to be dedicated to the public regardless ofwhether the element, component, or method step is explicitly recited inthe claims. No claim element is intended to invoke 35 U.S.C. 112(f),unless the element is expressly recited using the phrase “means for.” Asused herein, the terms “comprises,” “comprising,” or any other variationthereof, are intended to cover a non-exclusive inclusion, such that aprocess, method, article, or apparatus that comprises a list of elementsdoes not include only those elements but may include other elements notexpressly listed or inherent to such process, method, article, orapparatus.

What is claimed is:
 1. A fiber-reinforced thermoplastic hollowstructure, comprising: a shell comprising a first flange, a secondflange, and sidewalls, the shell comprising a fiber-reinforcedthermoplastic material; and a mating component coupled to the firstflange and the second flange and including a first internal surface, andthe first internal surface and internal surfaces of the sidewallsdefining a cavity, the first flange and the mating component defining afirst weld seam, the first weld seam being between 20% and 80% of alateral length of the first flange.
 2. The fiber-reinforcedthermoplastic hollow structure of claim 1, wherein the first weld seamis between 20% and 60% of the lateral length of the first flange.
 3. Thefiber-reinforced thermoplastic hollow structure of claim 1, wherein thesecond flange and the mating component define a second weld seam, thesecond weld seam being between 90% and 100% of a second lateral lengthof the second flange.
 4. The fiber-reinforced thermoplastic hollowstructure of claim 1, wherein at least one of the first flange and thesecond flange further comprises a plurality of stiffening ridges.
 5. Thefiber-reinforced thermoplastic hollow structure of claim 1, furthercomprising stiffening ribs disposed at least one of between the firstflange and an adjacent sidewall and between the second flange and anadjacent sidewall in the sidewalls of the shell.